Coatings for regulating transfer in photosensitive transfer elements



United States Patent 3,387,974 COATINGS FOR REGULATING TRANSFER IN PHOTOSENSITIVE TRANSFER ELEMENTS Wiiliam J. Duhnage and William A. Light, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey N 0 Drawing. Continuation-impart of application Ser. No. 552,720, May 25, 1966, which is a continuation-in-part of application Ser. No. 211,927, June 27, 1962. This application Feb. 8, 1967, Ser. No. 614,571

Claims. (CI. 96-28) ABSTRACT OF THE DISCLOSURE The photosensitive transfer material in a photographic transfer element is protected and its flow is regulated by a porous overcoat permeable to the photosensitive material in its transferable state.

This application is a continuation-in-part of copending US. Ser. No. 552,720 (now abandoned), filed May 25, 1966, which application in turn is a continuation-in-part of U.S. Ser. No. 211,927, filed June 27, 1962, now US. Patent 3,260,612, which application is a continuation-inpart of US. Ser. No. 124,037, now abandoned.

This invention relates to photographic elements and processes. In a particular aspect it relates to improvements in photosensitive transfer elements and processes involving the use of such elements.

In US. Patent 3,260,612, we described use of a continuous porous web as a means for regulating imagewise transfer of thermoplastic transfer material from a heatsensitive transfer element to a receiving surface. A porous permeable layer was coated on the surface of a heat-sensitive transfer element over a layer of thermoplastic transfer material, for example thermoplastic resin. These transfer elements are useful in thermoplastic printing processes. The particular thermoplastic transfer material which we described was activatable by heat to a state having reduced tackifying temperature. By preferentially heating only image areas of the element, the thermoplastic coating became transferable in those areas at a selected transfer temperature below the original tackifying temperature.

The porous permeable coating over the layer of transfer material improves the transfer element in several ways. It controls the flow of viscous transfer material from the heat-sensitive sheet to other surfaces. It reduces unwanted lateral spreading of the viscous transfer material during the transfer step. It protects the thermoplastic layer against abrasion and contamination. It prevents unwanted adhesion between the heat-sensitive surface and surfaces which come in contact with the element during manufacture, packaging, storage and use, etc., and in some embodiments it additionally provides a carrier for filter dyes, chemical reactants, half-tone patterns, opaquing grid patterns, etc.

A preferred porous permeable coating disclosed in the parent application was a continuous porous web of polyvinyl alcohol overlying the heat-sensitive layer. The porosity of the web is regulated to accommodate a wide variety of viscous thermoplastic transfer material by controlling the conditions of coating of the web forming material. A porous structure in the polyvinyl alcohol was provided by incorporating in the coating solution a pore forming agent, such as a metal salt or a surfactant, or in some embodiments both a salt and a surfactant. An improved porous structure in the polyvinyl alcohol layer is obtained by raising the temperature of the coating solution above a certain minimum temperature immediately upon application of the coating solution, and maintaining the temperature above this minimum until the porous structure has formed and the coating has substantially dried.

It is an object of the present invention to extend to additional types of image transfer elements the use of porous permeable overcoats as a means for regulating transfer.

It is a further object of this invention to provide new photosensitive image transfer elements.

It is another object of this invention to provide new photographic processes.

The present invention provides an improvement in transfer printing processes which comprise a step of transferring material to a receiving surface from a layer whose transfer characteristics have been altered or changed in photoexposed areas, and provides improved transfer elements for use in such processes. According to this invention, a transfer printing element comprising a support and a photosensitive layer of transfer material has coated over such photosensitive layer a porous layer which is permeable by such transfer material in its transferable state. This porous layer serves as a means for regulating or metering transfer of material from the transfer layer to a receiving surface. The porous permeable outer layer is functional with a variety of photosensitive printing elements of the kind having a photosensitive transfer coating, and the porous permeable layer may be composed of a variety of materials.

Examples of suitable photosensitive coatings which are operative in the practice of the present invention and transfer of which may be regulated by porous permeable overcoats include: thermoplastic coatings which comprise a thermoplastic resin vehicle in which is dispersed a photopolymerizable monomer, such as unsaturated esters of polyols, unsaturated amides, vinyl esters and unsaturated aldehydes, which polymerizes upon imagewise photoexposure and which is then transferred from unpolymerized areas; thermoplastic layers comprising a polymer which hardens by cross-linking on photoexposure, such as polyvinyl resins, unsaturated polyester resins and unsaturated polycarbonate resins, and which is transferred from unexposed areas; and silver halide-gelatin emulsion coatings which are hardened differentially in photoexposed areas by photographic development and then transferred from unexposed areas. Such photosensitive coatings are described in more detail in U.S. Patents 2,596,756, 2,610,- 120, 2,956,878, 3,030,208, 3,060,023, 3,060,026 and 3,- 100,702.

Examples of suitable porous permeable overcoats operative in the practice of the present invention to regulate or meter the transfer of thermoplastic material include: a microporous polymeric layer prepared by emulsifying an aqueous solution of a polymeric material such as gelatin, polyvinyl alcohol, or mixtures of such materials with a volatile water insoluble liquid and heating the emulsion to form a microporous polymeric layer; a fibril mat formed by dispersing agglomerated minute alumina fibrils modified by adsorbed acetate ions and optionally incorporating in the dispersion material such as agglomerated alumina fibrils, or colloidal silica; and a porous permeable polyamide layer which is precipitated and rendered porous by the unequal evaporation of different solvents.

For most practical processes, the support for the sensitive layer is preferably a flexible support such as paper, polyethylene-coated paper, polypropylene-coated paper, glassine, vegetable parchment, metal foils, or synthetic resin film bases such as poly(ethylene terephthalate) film base, polystyrene film base, cellulose acetate film base, cellulose acetate butyrate film base, cellulose nitrate film base, polyethylene film base, polypropylene film base, etc. However, the invention contemplates use of the combined photosensitive transfer layer and porous permeable overcoat with any practicable support. In some embodiments a separate support is not utilized, the photosensitive material being carried in a self-supporting binder.

Coating of the photosensitive material and the overcoat can be performed in any well-known manner, such as extrusion coating, hopper coating, dip coating, doctor blade coating, etc. Use of the porous overcoat permits greater coating thicknesses of photosensitive material without excessive transfer and loss of image definition. Typical coating densities of photosensitive material can range from about 0.2 to 3.0 grams per square foot, when dried. The preferred coating density for the porous overcoat layer is in the range of from about 0.3 to 0.7 gram per square foot, when dried. In this range the overcoat provides adequate flow control of the photosensitive material without unduly interfering with its transfer.

When the photosensitive element is intended for use in processes in which photoexposure occurs by light reaching the coated face of the element, the overcoat must be at least partially transparent to actinic radiation. With other elements intended for use in processes involving exposure through the film base, the porous permeable overcoat does not necessarily need to be transparent to actinic radiation.

Processes employing our photosensitive element can utilize either transmission exposures or reflex exposures. In processes using transmission exposure, the photo2ensitive element is placed in contact with an original and light is passed from the source through the original to the element. In the image areas of the original, light is absorbed while in the non-image areas it is transmitted thus exposing the photosensitive element. In processes using reflex exposure the photographic element is placed in contact with an original and light is passed from the source through the element to the original. In the image areas of the original, the light is absorbed and in the non-image areas it is reflected back through the lightsensitive element, thus further exposing the non-image areas. Right reading or laterally reversed images can be obtained depending upon whether the back or the front of the light-sensitive element is in contact with the original.

In the imagewise transfer of material from the photosensitive element to a receiver sheet in accordance with the invention, the transfer operation is typically carried out by placing the coated surface of the exposed element in contact with the receiving sheet, passing the sandwich so formed between a pair of heated pressure rollers and then separating the element from the receiving sheet which now carries the transferred image.

The invention is further illustrated by the following examples of preferred embodiments thereof.

EXAMPLE 1 Polyethylene terephthalate/sebacatc (50:50 molar ratio) 5.4 Dichloromethane 24.6 Triethyleneglycol diacrylate 5.4 Anthraquinone 0.005

p-Methoxyphenol 0.005

The resulting solution is removed from the mill and 0.2 gram of l,1'-diethyl-2,2'-cyanine iodide is added to give the composition optical density. It is then coated on a 15- foot length of polyethylene-coated paper at a coverage of 0.5 gram per square foot and dried. Ten grams of alumina fibrils modified by adsorbed acetate ions are dispersed in 200 ml. distilled water in a blender. The dispersion is coated over one-half of the width of the sensitive layer at a dry coverage of 0.4 gram per square foot. After the coated dispersion has dried, there is left a porous coating of alumina fibrils which is permeable by the thermoplastic material in the undercoat in its transfer state. A portion of the resulting coating cut to approximately 8" x 10" size and having both overcoated and non-overcoated areas for purposes of comparison is exposed on the coated side through a line positive to light from a 275- watt mercury arc lamp for 60 seconds at 4 inches distance. The coated side of the exposed sample is placed in contact with a sheet of uncoated, calendered white paper stock and passed through the nip of steel rolls at a temperature of C. Eight successive transfers are made from the same element by repeating the transfer step. The overcoated side yields the better copies having more uniform density from point-to-point on any single copy and more uniform density from one copy to the next. There is also noticeable improvement in resolution in copies transferred from the overcoated side.

EXAMPLE 2 This example illustrates the invention using a fibril mat in which is dispersed agglomerated material. The following overcoat composition is prepared:

8% homogenized alumina fibrils modified by This composition is blended and coated at a dry coverage rate of 0.7 gram per square foot over one-half the width of a photosensitive element prepared as in Example 1. After driving a porous coating remains which is permeable to the thermoplastic material of the photosensitive composition in its transferable state. A portion of the resulting coating having both overcoated and nonovercoated areas is exposed and transferred as in Example 1. The overcoated area yields the better copies having more uniform density from point-to-point on any single copy and more uniform density from one copy to the next.

EXAMPLE 3 This example illustrates the invention using a photosensitive polyvinyl resin which cross-links upon photoexposure causing substantial increase in melting point at the photoexposed areas. The porous permeable layer is a perforated sheet. Transfer is made at a temperature above the melting point of unexposed areas of the sensitive coating and below the melting point of exposed crosslinked areas. The following photopolymerizable composition is prepared:

Polyvinyl cinnamate g 2.5 Chlorobenzene ml 25 Toluene -ml-.. 75 2,4,6-trinitroaniline g 0.25

The ingredients are mixed in a blender for 15 minutes. The order of adding the ingredients is not critical. The resulting resinous dope is coated evenly on a length of 8-inch Wide Folio Greaseproof Transparent Copy Paper (Rhindelander Paper C0.), at a solids coverage of 0.7 gram per square foot and dried by evaporation of the volatile solvents. A portion of the resulting photosensitive element is then covered with a porous permeable layer as follows: A 5 percent solution of polyvinyl cinnamate in toluene 75 percent chlorohenzene 25 percent is spray-coated onto a wax-coated glass plate. The coating is dried and exposed to white light through an 80 percent half-tone-dot screen until exposed areas are hardened. Unexposed areas of the polyvinyl cinnamate layer are then dissolved by carefully swabbing the coating with methyl ethyl ketone solvent. The resulting finely perforated layer of cross linked resin is then transferred onto the surface of the photopolymerizable layer of the element previously prepared. The element is heated to approximately 150 C. and the glass plate is pressed with its coated side against the coated side of the sensitive element causing adhesion between the sensitive layer and the perforated layer and the glass plate with its wax coating is easily stripped away. A portion of the resulting coating is then cut from the photosensitive element with part of its surface covered by the perforated layer and part uncovered. The coated side of the element is then exposed for 1 minute through a line transparency to light from a 35-arnpere white flame carbon are at a distance of 4 feet. The coated side is then placed in contact with the surface of a receiving sheet of polyethylene-coated paper and passed through the nip of steel rolls as in Example 1. Six transferred images are made by repeating the transfer step with the single sample. From the area covered with the porous permeable overlayer, six successive copies of good density are obtained. From the uncovered areas only the first four copies of rapidly decreasing density are legible.

EXAMPLE 4 This example illustrates the invention using an overcoat of porous polyvinyl alcohol of the kind described more particularly in US. Patent 3,260,612. An overcoat solution is prepared as follows: 8.6 g. of a 25 percent aqueous solution of sodium sulfate is stirred into 100 grams of 5 percent aqueous solution of polyvinyl alcohol which contains 0.1 gram of a surfactant (sodium salt of dialkyl ester of sulfosuccinic acid). The solution is blended and thoroughly mixed with 1.8 grams of powdered zinc oxide. This dispersion is then coated at a dry coverage of 0.4 gram per square foot over one-half the surface of a photosensitive element prepared as in Example 3. A portion of the resulting coating having both overcoated and nonovercoated areas is exposed and transferred as described in Example 3. The overcoated areas of the sample yields more copies of a more uniform density than the nonovercoated areas.

EXAMPLE 5 This example illustrates the invention using the photosensitive polyvinyl resin of Example 3 and a porous permeable layer which is prepared from a polyarnide resin precipitated by unequal evaporation of different solvents. An overcoat solution is prepared by mixing 22.5 ml. of a polyhexamethylene adipamide modified by sebacamide methylene units in 2977.5 ml. of 95 percent ethyl alcohol and heating to 60 C. To this mixture is added 750 ml. of ethylene glycol and 18.75 grams of colloidal silica. The resulting mixture is dispersed for 2 hours in a ball mill. This overcoat solution is coated at a dry coverage rate of 0.37 gram per square foot over one-half the area of a photosensitive element prepared as in Example 3. The resulting coating having both overcoated and non-overcoated areas is exposed and transferred as in Example 3. The overcoat-ed areas yield a greater number of satisfactory copies and copies having more uniform density than the non-overcoated areas.

EXAMPLE 6 This example illustrates the invention using as the photosensitive transfer layer a mixture of thermoplastic resin and cross-linkable polymer which hardens by cross-linking upon photoexposure. The porous, permeable layer is a gelatin coating rendered porous and permeable by the method of coating. For the sensitive coating two solutions are prepared, one of 24 grams polyethylene glycol (Carbowax 4,000) in 150 ml. water and a second consisting of 6 grams poly(vinyl acetate-3-azidophthalate) in 60 ml. of 0.5 percent ammonium hydroxide aqueous solution with 0.06 g. of Durol black dye (Color Index 26370, National Aniline Division, Allied Chemical Corp). The two solutions are thoroughly mixed by ball milling, and the mixture is then coated on the metal side of a length of 8-inch side aluminum-paper laminate at a coverage of 0.5 g. per square foot and dried. After drying, one-half of the width of the element is overcoated on the same side with a composition prepared as folows:

Milli'iiter Gelatin, 10 percent by weight in water 50 Ethylene glycol 1 Dihydroxydioxane, 10 percent aqueous solution 5 Triton X- surfactant 0.25

These ingredients are mixed for 15 minutes in a highspeed mixer at P. Then 40 ml. of ligroin (B.P. C.) is added and the mixture is thoroughly emulsinfied in a high-speed mixer. The emulsion is then coated over half the width of the coated side of the sensitive element and dried. Volatile components including water and ligroin evaporate leaving a porous gelatin overcoat. After the element is thoroughly dried, a portion of the resulting coating approximately 8 x 10 inches in size, having areas covered by the overcoat and areas not covered by the overcoat, is exposed through a line positive to light from a 95-ampere carbon are for 2 minutes at 4 feet distance. The coated side of the exposed element is placed in contact with the surface of an uncoated calendered whie paper stock receiving sheet and the two are passed through the nip of steel rolls maintained at 68 C. Eight successive transfers are made from the single element by repeating the transfer step. Transfers from the overcoated areas are uniform in density decreasing only gradually from one copy to the next. Sunccessive transfers from the areas of the element not covered by the porous permeable overcoat deeereases rapidly in density from one copy to the next and becomes illegible after only a few transfers. Triton X-100 is a surface active agent purchased from Rhm and Haas Co. (an octylphenoxypolyethoxyethanol). The porous structure of the gelatin overcoat probably is caused by emulsified particles of the volatile hydrocarbon which evaporate from the coating leaving a porous structure.

EXAMPLE 7 In this example the photosensitive layer is a photographic silver halide emulsion containing an incorporated hardening developer. Photoexposure and development by a hardening developer causes gelatin in exposed areas to harden and become nontransfera-ble. A photosensitive silver halide is prepared by first making three solutions: (A) Twenty-five grams gelatin dissolved in 1 liter water at 25 C.; (B) One hundred grams silver nitrate dissolved in 100 ml. water at 20 C.; (C) Thirty-five grams sodium chloride dissolved in 500 ml. water at room temperature. Solutions B and C are run into solution A simultaneously at a uniform rate over a period of about 10 minutes, solu tion B being introduced at a slightly slower rate than solution C. Then grams gelatin is dissolved in 1500 ml. of water at 40 0; pH is adjusted to 5.0. A solution in 250 ml. methanol of 25 grams 3,4-dihydroxydiphenol developing agent is incorporated in the emulsion by dropwise addition while stirring. Then 2 ml. of 10 percent formaldehyde solution is added and the emulsion is coated on a polyethylene-coated paper support. This light-sensitive element is then overcoated as follows: Fifty ml. of a 4 percent solution of gelatin in water is emulsified with n-hexane. The emulsion is heated to 40 C. and stirred rapidly for three minutes. This composition is 7 coated over one-half the width of the silver halide emulsion on the photosensitive element. After the coatings are thoroughly dried, the sensitive element is exposed in contact with a printed sheet by reflex exposure for ten seconds, to light from four 7-watt fluorescent tubes spaced close together, at a distance of 4 /2 inches. After exposure, the photosensitive element is processed in three percent aqueous sodium carbonate solution for seconds, then wiped with a squeegee, then pressed with its coated surface against a porous receiving sheet of 16 pound weight white paper and immediately stripped away. A transfer print remains on the receiving sheet. Successive copies are made by repeating the processing and transfer steps six times. Successive transfers from areas of the element which has been overcoated are more uniform in density from co y to copy and also more successive copies are produced from the overcoated side. In this example, the porous gelatin overcoat is accounted for by the same explanation given in Example 6. Dyed gelatin from the undercoat transfers through the porous coat to the receiving sheet. The porous gelatin outer layer does not transfer.

EXAMPLE 8 This example illustrates the invention using a photosensitive layer which hardens by cross-linking when exposed to light. The porous permeable overcoat is a resin layer, impermeable in printed-on areas by the transfer material, printed in a half-tone pattern over the sensitive coating. A layer of poly(tetramethylene cinnarnylidene malonate), prepared as described in Michaels U.S. Patent No. 2,956,878, issued Oct. 18, 1960, and sensitized with 3 percent by weight with methyl benzothiazolylidene dithioacetate and containing 5 percent of copper phthalocyanine is coated from a 7.5 percent solution in trichloroethylene onto a sheet of baryta coated photographic paper support to a dry thickness of about 8.5 microns. After the coating has thoroughly dried, a porous permeable overcoat is printed over the sensitive layer by means of a copper letterpress plate bearing a 300 liues-per-inch half-tone pattern having 20 percent open areas. The overcoat is printed over only one-half the width of the cinnamylidene malonate layer. The composition of the overcoat is a pentaerythrit0l-modified alkyd 100 percent resin lithographic ink vehicle. The printed overcoat is then allowed to dry for several days. A portion of the coating cut from the element so as to have areas overcoated and other areas not overcoated is exposed for 4 minutes to light at a distance cm. from a l25-watt Mazda mercury vapor lamp through a line positive transparency. The exposed sheet is then placed with its face against the surface of a sheet of bond paper and the two are passed through the nip of steel rolls heated to 150 C. When the sheets are separated, a transfer image is printed on the receiving surface. Ten successive transfers are made from the single element by repeating the transfer step. After several successive copies, the transfer image from the area not having an overcoat becomes illegible while images transferred from the overcoated side remain le ible for several additional copies.

'In the foregoing examples we have illustrated the invention using various types of photosensitive transfer printing material and using various types of porous permeable overcoats to illustrate, but not to limit, the scope we contemplate for the invention. The particular transfer layers and porous permeable overcoats used in the examples, and the particular combinations, are not intended to limit the scope of the invention and it is to be understood that various sensitive coatings and overcoats such as those illustrated in the examples are interchangeable to a large extent.

Although the invention has been described in considerable detail with reference to preferred embodiments thereof, modifications and variations can be effected within the spirit and scope of the invention as described above and as defined in the following claims.

We claim:

1. In a photosensitive transfer printing element comprising a support and coated thereon a photosensitive layer of transfer material which has an original tranfcr characteristic and which undergoes change to a different transfer characteristic in photoexposed areas of said transfer material, the improvement wherein said element further comprises a dry non-tacky porous layer over said photosensitive layer, said porous layer being sufiiciently permeable by said transfer material of said photosensitive layer in its transferable state to permit transfer of said transfer material through said porous layer without substantial transfer of said porous layer.

2. A photosensitive transfer element as defined in claim 1 wherein said transfer material is selected from the group consisting of a thermoplastic resin vehicle in which is dispersed a photopo-lymerizable monomer which polymerizes upon the imagewise photoexposure, a polymer which hardens by cross-linking on photoexposure, and a silver halide gelatin emulsion coating which hardens differentially in photoexposed areas on photographic development, and wherein said porous permeable layer comprises a continuous porous permeable coating of a material selected from the group consisting of polyvinyl alcohol, gelatin, alumina fibrils, and polyamide resins.

3. A photosensitive transfer element as defined in claim 1 wherein said transfer material comprises a thermoplastic material which undergoes change in melting point by photographic exposure.

4. A photosensitive transfer element as defined in claim .1 wherein said transfer material comprises a photographic silver halide emulsion which hardens differentially in photoexposed areas by photographic exposure and development.

5. A photosensitive element as defined in claim 3 wherein said thermoplastic material comprises a photopolymerizable monomer and undergoes change to a higher melting point by photopolymerization of said monomer.

6. A photosensitive element as defined in claim 3 wherein said thermoplastic material comprises a photocross-linkable polymer component and undergoes a change to a higher melting point by photocross-linking of said component.

7. A photosensitive element as defined in claim 1 wherein said porous permeable layer comprises a continuous porous permeable coating of polyvinyl alcohol.

8. A photosensitive element as defined in claim 1 wherein said porous permeable layer comprises a continuous porous permeable coating of gelatin.

9. A photosensitive element as defined in claim 1 wherein said porous permeable layer comprises a continuous porous permeable coating of alumina fibrils.

10. A photosensitive element as defined in claim 1 wherein said porous permeable layer comprises a polymeric resin layer finely perforated in a half-tone dot pattern, said resin layer being permeable by said transfer material in its transferable state through the perforations of said resin layer.

References Cited UNITED STATES PATENTS 8/1965 Burg 96-115 7/1966 Dulmage 9628 XR 

